1. Field of the Art
This invention relates to an image forming method of an electrophotographic type for use in a copying machine or a printer.
2. Description of Related Art
With the recent development of digital technologies, image formation based on the degital method has become dominant in the electrophotographic image forming method. The method of forming a digital image is based on the formation of a positive image from a dot image of e.g. of 400 dpi (number of dots per 2.54 cm) defined by small pixels. There is a demand for image quality enhancing techiques for faithfully reproducing such a dot image formed of small dots.
As one of the image quality enhancing techniques, there have been proposed an electrophotographic developer or an image forming method, in which the particle size distribution of a small particle-sized toner or a toner particle and the shapes of particles thereof are made uniform, using a polymerization toner. The polymerization toner is manufactured by uniformly dispersing a raw material monomer in an aqueous medium and then causing polymerization thereof. Therefore, it is possible to obtain toner which is uniform in particle size distribution, and shapes. However, toner particles of such a small particle-sized toner are mutually chohesive and strongly adhere to the photoconductor, which tends to degrade cleaning property, and cause defective cleaning, such as uneveness of halftone, toner filming, and curling of a cleaning blade. These problems make it difficult to put the technique into practice.
Further, when the toner reduced in particle size is used, there is a problem that the color difference between an image formed at an early stage of deveopment and an image formed after runnings tends to become large.
On the other hand, when a drum-shaped (cylindrical) eletrophotographic photoconductor is employed, the clearning blade more often than not jumps on the surface of the photoconductor drum the without smoothly sliding thereon, to cause chattering, and the chattering can cause resonance of the photoconductor drum to produce offensive noise. Particularly, when the small paritcle-sized toner is used and the cylindrical organic photoconductor is employed, the adhesion of the toner to the photoconductor increases, and the above-mentioned problems in cleaning are liable to occur. To overcome these problems, there has been proposed a method of insertig a filler, a vibration-restraining material, a noise-abosribing material, or the like, within the photroceptor drum, as in Jp-Jitsukaisho-62-127567A, Jp-Tokukaisho-63-271388A, Jp-Tokukaihei-02-118684A, Jp-Tokukaihei-03-44689A, Jp-Tokukaihei-03-45981A, Jp-Tokukaihei-05-188671A, Jp-Tokukaihei-08-146686A, and WO-00/49466. However, for the use of the small paricle-sized toner, no sufficient soultion to the above problems have been provided.
Further, when a contact-type charging device is empolyed which is reduced in the amount of generation of ozone and operates to charge the photorecetpor by bringing a roller type or blade-type member thereof into contact with the photoconductor, due to the additional load of the contact-type charging device, the above-mentioned problem of cleaning, such as the phenomenon of chattering, beocmes laible to occur. More specifically, due to resonance with the chattering phenomenon caused during cleaning, the photoconductor drum and the charging roller are vibrated to produe unsual noise. To overcome this problem, it has been proposed to put various kinds of inserts within the photoconductor drum, as proposed in Jp-Tokukaihei-05-35048A, Jp-Tokukaihei-06-19377A, and Jp-Tokukaihei-05-333615A. However, the chattering phonomenon which is liable to occur during cleaning or due to contact charging when a small paticle-sized toner is employed is not fully investated.